1. Field of the Invention
The present invention relates to an ophthalmic photographic apparatus having a plurality of photography modes and timing means for measuring the elapsed time since its start by a user command.
2. Description of the Prior Art
There are ophthalmic photographic apparatuses, such as a fundus camera, that are provided with a timer, which is started and stopped in accordance with the operation of a user (examiner), and which is capable of imprinting the time measured by this timer onto the taken image and storing such as electronic data. Such a timer is used, for example, in fluorescence photography to measure and record the elapsed time since a fluorescent agent was intravenously injected.
Meanwhile, an ophthalmic photographic apparatus is known that has a plurality of photography modes such as a mydriatic photography mode wherein a mydriatic agent is dropped into the eye to be examined; a non-mydriatic photography mode wherein the fundus is irradiated with infrared light for observation and photography without a mydriatic agent; a visible light-excited fluorescence photography (also designated as fluorescein angiography; FA) mode for taking a visible light-excited fluorescence image; and an infrared light-excited fluorescence photography (also designated as indocyanine green angiography; IA) mode for taking an infrared light-excited fluorescence image. It is known to constitute the ophthalmic photographic apparatus so that it is provided with a plurality of timers for the purpose of, for example, independently timing the plurality of modes, as is known from Japanese patent laid open publication No. 322800/96.
There are various problems with the relationship among the plurality of photography modes discussed earlier when managing a timer in an ophthalmic photographic apparatus. For example, there is the case wherein a timer has been started in a certain photography mode and is then temporarily switched to another photography mode. In such a case, various technical concepts can be considered for handling the started timer.
First, it is conceivable that, for example, the timer can be started and stopped only in a specific photography mode. With such a constitution, the timer can be used only in the required photography mode, and it therefore has merits in that the action of the timer is clear, the operation system is simple, and misoperation can be prevented. It is also conceivable that the timer is automatically stopped or reset upon transition to another photography mode, thereby enabling to omit the operation of explicitly stopping the timer.
On the other hand, there is a case wherein the timer is started in a fluorescence photography mode and this mode is switched temporarily to another photography mode. When returning again to the fluorescence photography mode, the user wants to perform fluorescence photography using the time measured by the timer that was previously started. However, it is not possible to meet the demand of such a user with a constitution that automatically stops and resets the timer when switching to another mode.
If, in such a case, a constitution having no automatic stop and reset mechanism is used, the user must always stop the timer if he or she started it. This causes inconvenience during normal usage.
With a system provided with a plurality of timers, as described previously, the operator can separately use those timers in accordance with the photography mode, thus solving the abovementioned deficiency to a certain extent. However, there are other problems, such as the increased complexity and cost of the apparatus due to the provision of a plurality of timers and independent displaying means, which make the operation confusing and difficult to understand, and the user will inadvertently view a timer display other than the one intended.
Although a timer function hold mode can be provided to solve such troubles, there is a problem in that the photographing operation procedure is complicated. For example, the mydriatic fluorescence photography is initiated with the timer function hold mode, and the mydriatic color mode is then performed. The original mydriatic fluorescence mode must be manually restored.
Particularly in the case of fluorescence photography, the work of the examiner or the operation procedure is complex even under normal circumstances, which increases the burden on the examiner. Accordingly, there is a strong demand for an ophthalmic photographic apparatus that is easy to operate.
It is therefore an object of the present invention to provide an ophthalmic photographic apparatus that can be constituted simply and at low cost, has a simple operation system, and can maintain the timing information of the timer as needed even while switching among a plurality of photography modes.